A blood pump assists the action of the heart of a patient whose circulatory system has failed. Therefore, if the function of the apparatus driving the blood pump stops, the patient will be adversely affected. If a perfectly artificial heart fails, then the function of the heart is completely lost. If an auxiliary artificial heart or a balloon pump fails, burden is suddenly imposed on the patient's weakened heart.
Accordingly, the frequency of troubles in blood pumps and driving apparatuses must be reduced. To cope with troubles in driving apparatuses, various means have been proposed. An apparatus disclosed in Japanese Patent Laid-Open No. 136,352/1983 incorporates a battery and a pressure tank to make preparations for disconnection from an external power supply. An apparatus disclosed in Japanese Patent Laid-Open No. 207,668/1985 is equipped with a plurality of pressure sensors to monitor the waveform of pressure. In the techniques disclosed in Japanese Patent Laid-Open Nos. 169,463/1983 and 249,655/1987, two pressure-generating devices are mounted. If one of them fails, it can be switched to the other.
The prior art method of detecting trouble in a driving apparatus consists in detecting the output pressure, comparing the detected pressure with a preset pressure, and regarding the apparatus as defective if there is a great difference between them. For example, in the techniques disclosed in Japanese Patent Laid-Open No. 249,655/1987, the period of pressure pulses and the level of pressure are checked.
In order to drive the blood pump according to the condition of the organism, it is necessary that the period or the duty cycle of pressure pulses can be varied. Accordingly, where a check is done to see if the pressure pulses are abnormal, it is necessary to determine the time at which the pressure is checked, considering the minimum period, the minimum duty cycle, and the maximum duty cycle that can be set.
Since the pressure pulses delivered from a driving apparatus have positive pressure and negative pressure alternately, immediately after the pressure is switched from the negative pressure to the positive pressure, the pressure does not rise quickly. Also, immediately after the pressure is switched from the positive pressure to the negative pressure, the pressure does not drop rapidly. Therefore, it takes long for the pressure to reach the set value after the pressure is switched to the negative or positive pressure. This time varies, depending on the pressure obtained before the pressure is switched, on the time for which the negative pressure is applied, and on the time for which the positive pressure is applied. For example, when the pressure is switched from a negative pressure to a positive pressure, if the negative pressure obtained before the pressure is switched is large, it takes a long time for the pressure to settle down to the preset positive value. Conversely, if the negative pressure obtained before the pressure is switched is small, then the pressure quickly rises to the preset positive value after the pressure is switched.
Because the waveform of the pressure is blunted in this way, when the pressure is checked, the pressure is not stable and so the detected pressure may deviate from the preset pressure. In some cases, if the driving apparatus is normal, it may be regarded as defective. Where the driving apparatus is used for a patient suffering from serious cardiac insufficiency, the operation of the apparatus should not fluctuate at all in normal condition.